Flexible electroluminescent laminated panel



Dec. 11, 1956 M. s. JAFFE v 2,774,004

FLEXIBLE ELECTROLUMINESCENT LAMINATED PANEL Filed April 8, 1953 Inventor: Mary S. JaffQ Her Attorney United States Patent FLEXIBLE ELECTROLUMINESCENT LAMINATED PANEL S. Jafie, Cleveland Heights, Ohio, assignor to General ElectricCompany, a corporation of New York Application April 8, 1953, Serial No. 347,575

2 Claims. (Cl. 313-408) This invention relates in general to electroluminescent devices and more particularly to a laminated electroluminescent panel of. a flexible nature and suitable for working or forming into complex shapes.

In-the production of light by electroluminescence, a suitable phosphor issubjected to an electric field and the. light isgenerated directly, apparently by the eifects of moving electric charges within the crystals of-the phosphor. A form of electroluminescent device which holds forth considerable promise comprises a phosphor dispersed throughout. a thin layer of dielectric material sandwiched .etween two conducting plates or surfaces between which atvoltage is applied to excite. the phosphor. In order to make use of the light generated in the phosphor, oneof the conductive plates must be transparent or at least lighttransmitting. and the material which has been commonly used for thispurpose up to the present time is so-called conducting glass.

Conducting glass as presently made isglass having on one surface thereofan electrically conducting iridized metal oxide film integrally united with the surface, suitable metal-s being tin, indium, and cadmium, either alone or in combination. Such however sufier from all the mechanical disadvantages inherent in the. use of sheet glass, namely excessive weight, fragility, and ditficulty of forming into odd shapesand patterns. It.will thus readily be appreciated that such electroluminescent panels electroluminescent panels are not suitable for large electroluminescent devices such as architectural lamps, or for complexly shaped devices such as switch plates, illuminated symbols, and instrument panels.

An object of the present invention is to provide a new and improved form of electroluminescent panel having the advantages of lightness and flexibility.

Another object of the invention is to provide an electroluminescent panel which can readily be formed or bent into various shapes and designs during the installation thereof.

In accordance with the invention, I have found that it is possible to construct an electroluminescent panel wherein the transparent conductive plate which, up to the present, has generally been conducting glass, is a flexible conductive sheet of compacted glass fibers in the form of conducting glass cloth or paper. The glass cloth or paper is made conductive by subjecting it at a high temperature to the action of chemicals including in salt form one of the metals earlier mentioned which decomposes to form a conductive film integrally united with the surface of the glass fibers.

For a better understanding of the invention and of the advantages which may be realized through it, attention is noW directed to the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawing. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

The single figure of the drawing is a perspective view,

- process and composition.

"" 2,774,004 Ce fiat ated Dec. 11,-11956 2i partly fragmentedialong one edge, of an electrolumines cent panel embodying the-invention, the thickness of-the various layers comprised-in itbeing exaggerated for ease of visualizing.

A tactor which has; up until the present time, limited electroluminescentdevices to rigid-panels is the facti that the metal oxide films which'provide'electrical conduc tivity combined with optical transparency or' translu cency, require'h-igh temperatures of formation. For-in stance, glassmay be iridized with coatings of tin, indium, cadmium; and zinc baseoxides, but inorder to obtain' ap preciable conductivity with any of these formulations, the temperature ofthe glassmust be raised toatlleast-400" C. In fact, optimum conductivity'is'generally found in the-range of 600 C. orhigherl To the 'bestof my-knowl edge; there is no organic transparentplastic sheet which can' be" exposed 'tosuch temperatures without destruction or at least greater damage than'can betolerated,.so that transparentplastic-sheets offer of. themselves no solution to the-problem.

In accordance with my invention, I useglass in a' fiexi-' ble fibrousforin and make it conductive'by coating-the fiberswith an appropriate salt of tin, indium, cadmium, zinc or other semi-'conductingba'se; For' instance the glass fibers may. be drawn. atatemperature of approXi-" mately 6G0 C. througlian atmosphere of anhydrous sta-nnic tetrachloride '(SnCLr). vaporized in the usual mannerby: a'strea'mof air passed through it. Other suitable saltsmay be-mixturesof cadmium nitrate (Cd'(NOa)2) and indium trichloride (Incl-3). dissolved in water and may then be: made into cloth: orpaper.

strands into yarn whichayarni is subsequently woven 'in the usualifashion'into cloth; It will be appreciated'thatit is alsoipossible to first'make thefiber into the finished paper or cloth asthe case may be;and to subsequently spray the paper orcl'oth in order to'render'it conductive.

A preferred method of making conductive a fibrous glassy material, be' iiClOthj'Ol' paper, consists in dipping the material in a solution of a metal salt, which upon subsequent drying and baking, forms a conducting coating. A suitable solution may consist of indium basic trifluoracetate In (OH) (CFaCO2)2 with stannic chloride (SnClr) dissolved in an organic solvent such as ethylene glycol monoethyl ether acetate (Cellosolve acetate of Carbide and Carbon Chemicals Corporation). Reference may be made to my copending application No. 347,617, filed April 8, 1953, entitled Conductive Coating on Glass, and assigned to the same assignee as the present invention, for a more complete description of this The dipping process has the advantage that the metal salt solution is drawn by capillary action into the spaces between the fibers, so that the conducting coating envelopes the individual fibers of the cloth or paper, resulting in a higher conductivity or lower resistance per square.

Using a fibrous glassy material which has been rendered conductive by iridizing, an electroluminescent panel may be constructed as illustrated in the drawing. The lighttransmitting conducting surface of the cell is provided by the iridized glass cloth 1. The cloth may be iridized substantially on the lower side only when a spraying process is used, or it may iridized on both sides and throughout the body of the fibers or strands when a liquid dipping process is used, a higher conductivity per square being obtained with the latter process. The other conductive plate of the panel is provided by a thin layer of metal 2 which may be adherent to a backing panel 3 of plastic, for

instance aluminum deposited by the usual vacuum evaporation process. It will be appreciated that since transparency or translucency is not a requirement for the lower plate of the panel, a variety of materials may be utilized for it, such as metallized or metal-clad plastics or plywood, or:a thin metal sheet. Alternately of course, the lower plate may be a second sheet of conducting fibrous glassy material such as the glass cloth 1, where it is desired that the panel radiate light from both sides.

The" phosphor is comprised in a layer 4 sandwiched between the glass cloth 1 and the metallized layer 2 and it may takethe form of a zinc oxide-zinc sulfide phosphor with suitable activators such as copper, manganese, lead or silver, fired at'a temperature in the range from 700 C, to 1200? C. A number of electroluminescent phosphors are at present known to the artand any of these may be utilized in a cell construction within the purview of my invention. Reference may be made to copending application serial 'No. 266,241, filed January 12, 1952, ofiHerman C. Froelich,'entitled Preparation of Electroluminescent Phosphors, and assigned to the same assignee as the present invention, for a description of a. suitable electroltuninesc'ent phosphor and a detailed disclosure of the method of its preparation. The phosphor material inay be dispersed throughout a suitable solid dielectric to constitute the layer 4, the dielectric material serving at the same time as a cement making the phosphor adherent to the glass cloth 1 and to the metallized layer 2, whereby these electrically active layers-of the panel are tightly bound together as a laminate. Where it is necessary toprotect the panel from the efiects of the atmosphere such as moisture or dust, the glass cloth 1 may be faced with a layer 5 of transparent plastic. Suitable transparent plastics for this purpose may for instance be methyl-methacrylate, cellulose esters and ethers, urea formaldehyde, and phenol condensation products. The edge of the panel may be sealed by a molding 6 of similar material glued on either side to the outer plastic plates 5 and 3'of the pane-l. Metal tabs 7 and 8 may be provided to serve as terminals for the application of voltage to the cell, the former being extended around'the inside of the moulding into an area of contact with the conductive glass cloth 1, and the latter'being likewise extended into an area of contact 'with'the metal or metallized layer I While the illustrated embodiment of the invention has been shown as comprising a conductive glass cloth, it will be appreciated that conductive glass paper may likewise be used.

My invention thus provides an electroluminescent panel which has the advantages of flexibility, light weight, mechanical strength, and the ability to be punched, drilled, sawed and bent as desired. While the reticular nature of the conductive glass cloth 1 may result in a somewhat lower electric field on the phosphor lying opposite a hole in the mesh with corresponding loss of luminous output, the loss is not serious and is small'in amount, particularly in the case of fine woven cloth or in the case of glass paper where the fibers are laid very close together.

While a certain specific embodiment of the invention has been shown and described, it is intended as exemplary and not as limitative of the invention. The scope of the invention is to be determinedby the appended claims which are intended to cover any modifications coming within its true scope and spirit.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A flexible electroluminescent panel comprising a flexible fibrous glass sheet made of glass fibers individually enveloped in a light-transmitting electrically conductive coating formed thereon, a layer thereover of an electroluminescent phosphor dispersed in a dielectric mate rial adherent to said sheet, and a layer thereover of a conductive material adherent to said dielectric material.

2. An electroluminescent panel comprising a fibrous glass sheet made of glass fibers individually enveloped in formed thereon, a layer thereover" of an electroluminesa light-transmitting electrically conductive coating cent phosphor dispersed in a dielectric material adherent to said sheet, a layer thereover of a conductive material adherent to said dielectric material, and a protective lighttransmitting sheet of plastic material on the reverse side of said glass sheet from the aforesaid layers.

References Cited in the file of this patent UNITED STATES PATENTS Mager Sept. 4, 1951 2,624,857 Mager Jan. 6, 1953 2,644,113 Etzkorn June 30, 19531 

